PHP Arrays (Cont.)

Associative Arrays (Cont.)
If the ID key of an associative array is a string, it could be doubly quoted or singly quoted. 

 <html><body>
 <?php
   $hash["ID"] = 10;
   $hash['ID'] = 20;
   echo $hash["ID"] + $hash['ID'];
 ?>
 </body></html>
output =




†According to the Stack Overflow, using array key names without quotes is a legacy feature in PHP. It was originally the way to do it, but it is no longer recommended and is only still supported for backward compatibility.

Multidimensional Arrays
In a multidimensional array, each element in the main array can also be an array. And each element in the sub-array can be an array, and so on. The arrays could be associative arrays too. It seems variable interpolation does not work for a multidimensional array element. For example, 
   echo  "$families[$arr2][$i]<br />";
is not working. You have to use the following command instead: 
   echo  $families[$arr2][$i] . "<br />";
 <html><body>
 <?php
  $size = 
  for ( $i=0; $i<$size; $i++ )
    for ( $j=0; $j<$size; $j++ )
      $arr[$i][$j] = ;

  $total = 0;
  for ( $i=0; $i<$size; $i++ )
    for ( $j=0; $j<$size; $j++ )
      $total += $arr[$i][$j];
  echo  $total;
 ?>
 </body></html>
Output =   
 <html><body>
 <?php
  $families = array (
    "Griffin" => array (
      "Peter",
      "Lois",
      "Megan"
    ),
    "Brown" => array (
      "Glenn",
      "Andrew",
      "Ella"
    )
  );
  echo  $families[][];
 ?>
 </body></html>
Output =




      What did the baby corn ask the mama corn?    
      “Where’s Pop corn?”